Milestone Function to restrict activity release

Hi,

I have created three activities. (10,20,30)

When I am releasing the full project / network I want to restrict the release of 20 and 30 and want to release only activity 10.

When I am confirming the activity 10 then 20 should be release and when confirming 20 then 30 should be release.

I have tried by using milestone functions but it is not working.

Can anybody please tell me how to do the same by using milestone functions step by step.

Regards,

Pradeep